1. Field of the Invention
This invention concerns improvements in and relating to detectors, particularly, but not exclusively, in relation to the detection of ions produced by alpha emissions and in conjunction with beta emission detection and/or the mounting of such detectors.
2. Present State of the Art
It is desirable to have as much information as possible about the location and type of emission sources encountered in a variety of applications, including decommissioning and waste management operations.
Separate instruments for alpha emissions and beta emissions are known. For instance, direct detection of alpha emissions can be achieved by the presentation of the detector in very close proximity with the source to be measured or ions produced by the passage of alpha particles can be detected by attracting them to detector plates. However, use of two separate instruments involves two separate, time consuming, analyses of an area and also introduces difficulties in tying the two sets of information together to give accurate positional resolution. Additionally, whilst it is desirable to apply such techniques to a wide variety of instrument forms, for instance instruments which are moved about during monitoring. Vibration, what ever its source, be it from movement of the instrument or due to the presence of motors etc, gives rise to substantial problems.
The present invention aims to provide an instrument and detector type in which combined alpha and beta determination in a single simultaneous step is achieved, from corresponding locations, and without effecting detector efficiency in relation to either type of source. The present invention also aims to provide for the elimination or substantial reduction of vibration using mechanical means.
According to a first aspect of the invention we provide an instrument for monitoring alpha and beta sources, the instrument position determining a detecting location, the instrument comprising one or more detector elements, at least one of the detector elements providing an electrically conducting exterior portion and beta detector means provided behind that portion relative to the detecting location, the electrically conducting layer being provided with an electrical potential, means being provided to monitor ions discharged on the element.
In this way a single detector can monitor ions produced by alpha particles and also directly monitor beta particles entering the beta detector means.
The instrument may be used to monitor discrete items or areas. Discrete items are typified by tools, pipes, pumps, filters and the like. Areas are typified by locations or surfaces, such as floors, walls, ceilings, soil, rubble, material on a conveyor, and include surfaces of pieces of equipment such as glove boxes, tanks, vessels and the like.
The item or area may be presented to the detecting location by moving the item or area to the location and/or by moving the instrument to the item or location. Movement of the item or area will be prefer for small items and conveyed material. Movement of the instrument may be preferred for surveying surface areas, for instance soil, or for monitoring large items which cannot readily be moved.
The detection location may be provided within a continuous enclosure formed by the instrument, for instance a sealable box. The detecting location may be provided within an open enclosure and/or at or in proximity to an opening in the enclosure, for instance in proximity to a hood.
The element(s) may be planar. The element(s) may be non-planar.
Two or more elements may be provided. The elements may be provided in opposition to one another, for instance with the detecting location between them.
The alpha detecting means are preferably provided by the electrically conducting portion. Detection is preferably indirectly made through detection of ions.
Preferably the electrically conducting portion is of metal. Aluminium represents a preferred metal for the portion.
The conducting portion preferably extends at least across the part of the element facing the detecting location. It is preferred that the conducting portion extends around the beta detection means.
The conducting portion may be provided with a greater thickness for portions not opposing the detecting location, particularly those portions facing away from the detecting location. The back face of a planar element may, therefore, be provided with a thicker layer of conductor, for instance greater than 1 mm.
The conducting portion may be provided with a thickness, opposing the detecting location, at least in part, of less than 100 xcexcm, preferably less than 50 xcexc and ideally less than 10 xcexcm.
The beta detecting means may comprise a scintillator. The scintillator may be formed of a plastic scintillating material in conjunction with a photodetector, for instance a photomultiplier. Preferably the scintillator material is light sealed relative to the outside of the scintillator. The sealing may be provided in part, or completely, by the electrically conducting material.
The beta detector means may comprise a detector in which the presence of beta particles generates ions, for instance a gas flow proportional counter. The detector means may be provided, completely or in part, with a metallic exterior by the electrically conducting portion.
The electrical signal generated by the alpha detector means is preferably conveyed to monitoring means by an electrical conductor. The monitoring means may comprise an electrometer.
Preferably the electrical potential is applied from an external potential source. The electrical potential may be electrostatically provided.
Where only one element is provided an electrical potential is preferably applied to that element.
Where more than one element is provided some or all of those elements may have, or have applied, a potential. The potentials may be different. Some of the elements may be grounded, with some having a potential. Preferably the different potentials are configured to generate an electric field between adjoining elements. Preferably in such a case the detection location is provided between the elements.
The ion discharge monitoring means may comprise an electrostatic potential determination. Preferably the means comprise current indicating means.
The current indicating means preferably includes current measuring means, for instance an electrometer, such as a ground referenced electrometer.
Where only one element is provided the current indicating means is connected to that element.
Where two or more elements are provided the current indicating means may be connected to one or more of those elements. Preferably elements of the same applied potential are connected to the current indicating means.
The element may be provided with a further electrically conducting portion, electrically insulated relative to the first and provided on a side facing away from the detecting location. The further conducting portion is preferably at an equivalent level of applied potential to the first. Preferably current indicating, and most preferably current measuring means are connected to the further conducting portion.
The further electrically conducting portion is preferably in contact with a gas volume in contact with the gas of the detecting location. Preferably the gas contacting the further electrically conducting portion is separated from the gas volume in contact with the detecting location by an ion and/or particulate impermeable barrier.
Preferably a further beta detection means is provided between the further electrically conducting portion and the first beta detection means. Preferably the two beta detection means are separated by a beta screen.
According to a second aspect of the invention we provide a detector element for monitoring alpha and beta sources, the element comprising an electrically conducting exterior portion for receiving ions generated by alpha particles and beta detector means provided behind the electrically conducting portion relative to the source(s).
The element(s) may be planar. The element(s) may be non-planar. Cylindrical element(s) may for instance be provided.
Preferably the electrically conducting portion is of metal. Aluminium represents a preferred metal for the portion.
The conducting portion preferably extends at least across part of one side of the element. It is preferred that the conducting portion extends around the beta detection means.
The conducting portion may be provided with a greater thickness for portions on one or more sides than for portions on one or more other sides. One side may have a lower thickness than the opposing side and the adjoining sides. The thicker layer of conductor may be greater than 1 mm.
The beta detecting means may comprise a scintillator. The scintillator may be formed of a plastic scintillating material in conjunction with a photodetector, for instance a photomultiplier. Preferably the scintillator material is light sealed relative to the outside of the scintillator. The sealing may be provided in part, or completely, by the electrically conducting material.
The beta detector means may comprise a detector in which the presence of beta particles generates ions, for instance a gas flow proportional counter. The detector means may be provided, completely or in part, with a metallic exterior by the electrically conducting portion.
The electrical signal generated by the alpha detector means is preferably conveyed to monitoring means by an electrical conductor.
The element may be provided with a further electrically conducting portion, insulated relative to the first, and provided on a side facing away from the first. Preferably a further beta detection means is provided between the further electrically conducting portion and first beta detection means. Preferably the two beta detection means are separated by a beta screen. Background alpha and beta determinations may be made in this way.
According to a third aspect of the invention we provide a method of monitoring alpha and beta sources, the method comprising the steps of placing a location to be monitored in proximity with an instrument, and/or placing an instrument in proximity with a location to be monitored, the instrument being provided according to the first aspect of the invention, the instrument providing a signal indicative of alpha sources and a signal indicative of beta sources.
The third aspect of the invention should be taken to include steps and stages necessary to implement the features set out elsewhere in this document, including those features, options and possibilities themselves.
According to a fourth aspect of the invention we provide an instrument for detecting ions originating from a monitored location, the instrument having a body portion defining a detecting location, the instrument comprising one or more electrically conducting detector elements, the element(s) having an electrical potential relative to the monitored location, at least a part of the one or more electrically conducting element(s) opposing the detecting location and one or more of the elements being mounted on an electrically insulating material to insulate it relative to the body portion, the element(s) being in contact with the mounting over at least 10% of the surface area of the element facing away from the detecting location and further comprising means for monitoring ions discharged on one or more of the elements.
The contact area may comprise at least 25%, more preferably at least 50% and ideally at least 75% of the area of the element facing away from the detecting location. Preferably the element is in contact with the mounting over all, or substantially all, of the side facing away from the detecting location.
The instrument may be used to monitor discrete items or locations. Discrete items are typified by tools, pipes, pumps, filters, cables, rods and the like. Locations are typified by surfaces, such as floors, walls, ceilings, soil, rubble, material on a conveyor, and include surfaces or parts thereof on pieces of equipment such as glove boxes, tanks, vessels and the like.
The item or location may be introduced to the detecting location by moving the item or location to the location and/or by moving the instrument to the item or location. Movement of the item or location will be preferred for small items and conveyed material. Movement of the instrument may be preferred for surveying surface areas, for instance soil, or for monitoring large items which cannot readily be moved.
The instrument may provide the detecting location within a continuous enclosure, for instance a sealable box. The instrument may provide the detecting location within an open enclosure, for instance in proximity to a hood.
Ions generated by the item and/or location may be moved to the detecting location, for instance by air flow, from a monitored location.
The element(s) may be planar. The element(s) may be non-planar.
The mounting may be planar. The mounting may be non-planar.
Preferably the insulating mounting is provided in a configuration matching the portion of the element to which it is to be attached. A planar element and planar mounting are preferred.
The mounting may be attached to the instrument around one or more, and preferably two or more, edges.
The mounting may be attached to the instrument on one side, preferably the side facing away from the detecting location.
The contact between the mounting and the instrument may be provided over at least 10% of the surface area of the mounting. The contact may be at least 10% of the surface area of the side of the mounting facing away from the detecting location. The contact area may comprise at least 25%, more preferably at least 50% and ideally at least 75% of the area of the mounting facing away from the detecting location. Preferably the mounting is in contact with the instrument over all, or substantially all, of the side facing away from the detecting location.
Two or more elements may be provided. The elements may be provided in opposition to one another. Preferably in such cases the detecting location is provided between the elements.
Preferably the electrically conducting element is of metal. Aluminium represents a preferred metal.
Preferably the electrical potential is applied from an external potential source. The electrical potential may be provided electrostatically.
Where only one element is provided an electrical potential is preferably applied to that element.
Where more than one element is provided some or all of those elements may have, or have applied, a potential. The potentials may be different. Some of the elements may be grounded, with some having a potential. Preferably the different potentials are configured to generate an electric field between adjoining elements, and most preferably with the detecting location with the electric field.
The current indicating means preferably includes current measuring means, for instance an electrometer.
Where only one element is provided the current indicating means is connected to that element.
Where two or more elements are provided the current indicating means may be connected to one or more of those elements. Preferably elements of the same applied potential are connected to the current indicating means.
The mounting may include leakage current protection/guard. The protection/guard may comprise an electrical conductor isolated electrically from the detector element(s) by part of the insulating mounting, the further electrical conductor being provided between the detector element(s) and the mounting on the instrument body. Preferably the further conductor is also electrically insulated from the instrument body by a further electrical insulating component provided between the further conductor and the mounting on the body. The contact between the further conductor and insulating mounting for the detector element(s) and/or the contact between the further conductor and the further electrical insulating component may also be provided according to the invention in terms of the contact area.
The element may be provided with a further electrically conducting detector element, insulated relative to the first and relative to the body, and provided on a side facing away from the detecting location. The further portion is preferably at an equivalent applied potential level to the first. Preferably current indicating, and most preferably current measuring means are connected to the further portion.
The further detector element may also be provided with leakage protection a guard plate as described above.
In a preferred structure a detector element facing the detecting location is provided, with a further detector element mounted indirectly thereon facing away from the detecting location, the indirect mounting be provided by the electrical insulated mounting and comprising a first electrical insulator mounted on the detector element, an intervening element mounted on the first insulator, a second insulator mounted on the intervening element, the second insulator mounting the further detector element. Preferably this structure is mounted on the instrument body via the intervening element. Preferably the intervening element is electrically conducting.
According to a fifth aspect of the invention we provide a method of detecting ions generated by one or more alpha sources, in which an instrument is provided in proximity with a location receiving ions generated by an item and/or location which may or may not have an alpha source and monitoring the level of ions detected, the instrument being provided according to the first aspect of the invention.
The method may include moving the instrument between monitoring different items and/or locations.
The fifth aspect of the invention should be taken to include steps, stages and operations necessary to implement the features, options and possibilities set out elsewhere in this document.